Half-sandwich trihydrido ruthenium complexes
Alexandr L. Osipov
a, Dmitry V. Gutsulyak
a,b, Lyudmila G. Kuzmina
c,
Judith A.K. Howard
d, Dmitry A. Lemenovskii
a, Georg Su¨ss-Fink
e, Georgii I. Nikonov
a,b,*aChemistry Department, Moscow State University, Vorob’evy Gory, 119992 Moscow, Russia
bChemistry Department, Brock University, 500 Glenridge Ave., St. Catharines, ON, Canada L2S 3A1
cInstitute of General and Inorganic Chemistry, RAS, Leninskii Prosp. 31, 119991 Moscow, Russia
dChemistry Department, University of Durham, South Road, Durham DH1 3LE, UK
eInstitut de Chimie, Universite´ de Neuchaˆtel, Case Postale 158, CH-2009 Neuchaˆtel, Switzerland, UK
Abstract
This paper reports facile preparation of half-sandwich trihydrido complexes of ruthenium based on the reactions of the readily avail- able precursors [Cp(R3P)Ru(NCCH3)2][PF6] with LiAlH4. The target complexes were characterized by spectroscopic methods and X-ray structure analysis of CpðPhPri2PÞRuH3.
Keywords: Ruthenium; Hydride
1. Introduction
Half-sandwich complexes of ruthenium find multiple applications in chemistry as effective catalysts [1] and as platforms to support unusual metal–ligand and ligand–
ligand bonding [2–5]. Our interest in this field stems from the observation that the CpLRu fragment (where L is a two-electron donor) is formally isolobal with the Cp2M (M = Nb, Ta, Ti), Cp(RN)M (M = V, Nb, Ta) and (RN)2M (M = Mo, W) moieties [6] which were found to support a variety of H. . .SiX and H. . .GeCl interligand interactions [7–10]. Given the fact that Group 5 trihydrides Cp2MH3(M = Nb, Ta) are readily available [11] and are very useful starting points in the chemistry of Group 5 met- allocenes [12], we expected that ruthenium trihydrides Cp(R3P)RuH3 would exhibit an analogously rich chemis-
try. Apart from their potential synthetic utility, ruthenium trihydrides are also of interest because of their propensity to manifest quantum-mechanical exchange coupling [13].
Previously, only one trihydride complex with unsubsti- tuted Cp ring, Cp(Ph3P)RuH3 (1a), has been reported [14]. By contrast, a family of permethyl substituted com- plexes Cp*(R3P)RuH3 (Cp*@C5Me5) is well described [15], including the X-ray structure of Cp*(Ph3P)RuH3
[16]. Complex1ais a classical trihydride [16], whereas the isolobal tris(pyrazolyl)borate complex Tp(Ph3P)RuH(g2- H2) exist in a hydride(dihydrogen) form [17], underpinning the strong effect of the ring on the extent of Ru–H interac- tion. Here, we report facile general access to a series of complexes Cp(R3P)RuH3 (R3P@Ph3P (a), Ph2PriP (b), PhPri2P (c) and Pri3P (d)) and the crystal structure of com- plex Cp(Ph2PriP)RuH3.
2. Results and discussion
Davis et al. previously reported that reaction of Cp(Ph3P)2RuCl with LiAlH4in THF affords a 4:1 mixture
* Corresponding author. Address: Chemistry Department, Brock Uni- versity, 500 Glenridge Ave., St. Catharines, ON, Canada L2S 3A1.
Tel.: +1 905 6885550x3350; fax: +1 905 9328846.
E-mail address:gnikonov@brocku.ca (G.I. Nikonov).
of Cp(Ph3P)RuH3and Cp(Ph3P)2RuH, from which the for- mer complex can be isolated by recrystallization from ether [14]. In our hands, however, difficult-to-separate mixtures of variable ratios of Cp(Ph3P)RuH3 and Cp(Ph3P)2RuH were produced. Attempts to extend this approach to the preparation of other complexes Cp(R3P)RuH3by reacting the mixed phosphine precursors Cp(R3P)(Ph3P)RuCl [18]
with LiAlH4 lead to mixtures containing predominantly the monohydrides Cp(R3P)(Ph3P)RuH.
The related permethyl substituted complexes Cp*- (R3P)RuH3(Cp*– pentamethylcyclopentadiene) have been previously prepared by the reaction of Cp*(R3P)RuCl2with NaBH4in ethanol [15a], with LiBHEt3in THF [15b] and by dihydrogen addition to the 16e compound Cp*(R3P)RuOR [15c]. None of these precursor chloride or alkoxide compounds are available for the fragment Cp(R3P)Ru yet.
We designed an alternative strategy to the half-sandwich Ru trihydrides based on the reaction of cationic complexes [Cp(R3P)Ru(NCCH3)2][PF6] (2a–d) (Scheme 1) with LiAlH4. The key starting material, the compound [CpRu- (NCCH3)3][PF6] (3), has recently become available through the contribution of Ku¨ndig et al. [19], which opens a new facile route to the vast chemistry of the cation [CpRu(NCCH3)3]+[1a,20]. Reactions of3with an equiva- lent of phosphine R3P allow for easy preparation of the cor- responding exchange products [Cp(R3P)Ru (NCCH3)2] [PF6] (2a–d) characterized by NMR and IR spectroscopy (Scheme 1) [21]. In particular, the N„C triple bond gives rise to a band in the IR spectrum at 2276 cm1, whose position does not depend on the type of phosphine ligand being present. Treatment of these precursors with LiAlH4 in THF followed by quenching the reaction mixture with degassed water affords, after work-up, the trihydrides Cp(R3P)RuH3(1a–d) in good yields.
The new trihydrides 1b–d and the previously reported complex Cp(Ph3P)RuH3(1a) were characterized by NMR and IR spectroscopy, and by X-ray structure of the com- pound1b. Like in their Cp*analogues, at room temperature the hydrides in1a–dgive rise to one, averaged hydride sig- nal in the region between 10.3 and 11.3 ppm coupled with the phosphine. The IR spectra show corresponding Ru–H bands in the region 2010–2001 cm1.
The molecular structure of complex 1b is shown in Fig. 1. Spectroscopic data for the related compound Cp(Ph3P)RuH3 (1a) have been previously rationalized in terms of a classicalC3vstructure, with the bulky phosphine occupying a position trans to the Cp ring and the three
hydrides forming an equatorial plane in a pseudo-TBP structure [14]. In fact, the experimental geometry of 1bis similar to that one of the analogous complex Cp*(Ph3P)RuH3, which can be better described as a four- leg piano-stool [15a]. The CNT-Ru and Ru–P vectors, where CNT is the centroid of the Cp-ring, form an angle of 125.7. Surprisingly enough, although less steric interac- tion of phosphine with the ring could have been antici- pated, the Ru-CNT distance of 1.927 A˚ in 1b is slightly longer than the corresponding parameter in the more crowded complex Cp*(Ph3P)RuH3 (1.91 A˚ ) [22]. By way of contrast, the Ru–P bond lengths of 2.2465(4) A˚ in 1b is shorter than the Ru–P distance in Cp*(Ph3P)RuH3
(2.252(1) A˚ ), probably due to a combination of a better donating phosphine and a less bulky Cp ring. These obser- vations can be explained in terms of interplay of bonding capabilities of a more donating phosphine and a less donat- ing cyclopentadienyl ring in 1b in comparison with Cp*(Ph3P)RuH3. The Ru–H hydride bond lengths, although subject to the well known uncertainty of finding
Ru NCCH3 NCCH3 CH3CN
+
PF6
PR3
Ru NCCH3 NCCH3 R3P
+
PF6
1) LiAlH4 in THF 2) H2O
Ru H R3P H H
Scheme 1. Preparation of [Cp(R3P)Ru(NCCH3)2][PF6] and Cp(R3P)RuH3.
Fig. 1. Molecular structure of complex1b. Selected molecular parameters (bonds in A˚ , angles in ): Ru(1)–P(1) 2.2465(4), Ru(1)–H(1) 1.50(3), Ru(1)–H(2) 1.54(3), Ru(1)–H(3) 1.55(3), P(1)–C(15) 1.8410(15), P(1)–C(9) 1.8426(16), P(1)–C(6) 1.8659(16), and P(1)–Ru(1)–H(1) 74.7(10), P(1)–
Ru(1)–H(2) 96.5(10), P(1)–Ru(1)–H(3) 77.6(10), H(1)–Ru(1)–H(2) 64.4(14), H(1)–Ru(1)–H(3) 114.7(16), H(2)–Ru(1)–H(3) 61.7(14).
hydride ligands by X-ray diffraction, fall in a narrow range of 1.503–1.548 A˚ , which is typical for Ru–H bonds.
In summary, we describe a convenient general approach to the trihydride complexes Cp(R3P)RuH3and the X-ray structure of the complex Cp(Ph2PriP)RuH3. We are currently exploring application of these com- pounds to the synthesis of silylhydride derivatives of ruthenium.
3. Experimental
All manipulations were carried out using conventional high-vacuum or argon-line Schlenk techniques. Solvents were dried over sodium or sodium benzophenone ketyl and either kept under argon or distilled into the reaction vessel by high vacuum gas phase transfer. NMR spectra were recorded on a Bruker (1H, 300 MHz; 13C, 75.4 MHz) and Varian (1H, 400 MHz; 13C, 100.6 MHz;
31P, 161.9 MHz) spectrometers. IR spectra were obtained as Nujol mulls with an ATI Mattson FTIR spectrometer spectrometer. RuCl3*aq was purchased from Precious- Metals-on-Line, other reagents were from Sigma-Aldrich.
Complexes [CpRu(NCCH3)3][X] (X = PF6, BF4) [19] and phosphines were prepared according to the literature methods.
3.1. General procedure for the preparation of [Cp(R3P)Ru (NCCH3)2][BF4]: example of [CpðPri3PÞRuðNCCH3Þ2] [BF4] [23]
Solution of PPri3(0.161 g, 1.01 mmol) in CH3CN (20 mL) was added dropwise to a solution of [CpRu(NCCH3)3][BF4] (0.380 g, 1.01 mmol) in CH3CN (20 mL). The mixture was stirred for 3 h at ambient temperature. Concentration of the resulting yellow solution to 5 mL in vacuum and addition of 40 mL of diethyl ether precipitated the product in the form of yellow crystals. Yield: 0.470 g (94%). The cor- responding PF6salt was prepared with a similar yield. IR (Nujol): m(CN) = 2276 cm1. 1H NMR (CDCl3): d 4.50 (s, 5, C5H5), 2.39 (s, 6, CH3CN), 2.29 (d sept, J(H–
H) = 7.2 Hz, J(P–H) = 8.5 Hz, 2, P(CH(CH3)2)2), 1.18 (dd,J(H–H) = 7.2 Hz,J(P–H) = 13.2 Hz, 6, P(CH(CH3)2)).
31P NMR (CDCl3): d 56.0. 13C NMR (CDCl3): d 128.1 (CH3CN), 74.9 (Cp), 26.6 (d, J(P–C) = 18.7 Hz, P(CH (CH3)2)2), 19.7 (s, P(CH(CH3)2)), 4.0 (s,CH3CN). Elemen- tal analysis for ½CpðPri3PÞRuðNCCH3Þ2½PF6, C18H32F6
N2P2Ru (553.468). Anal. Calc.: C, 39.06; N, 5.06; H, 5.83.
Found: C, 38.84; N, 5.08; H, 5.79%.
3.2. [CpðPri2PhPÞRuðNCCH3Þ2][BF4]
This compound was prepared analogously to½CpðPri3PÞ RuðNCCH3Þ2½BF4, using PPri2Ph (0.232 g, 1.19 mmol) and [CpRu(NCCH3)3][BF4] (0.450 g, 1.19 mmol). Yield:
0.600 g (95%). The corresponding PF6salt was prepared with a similar yield. IR (Nujol): m(CN) = 2276 cm1. 1H NMR (CDCl3): d 7.55 (m, 2, o-Ph), 7.42 (m, 3, m-Ph and p-Ph),
4.47 (s, 5, C5H5), 2.56 (m, 2, P(CH(CH3)2)2), 2.41 (s, 6, CH3CN), 1.08 (dd, J(H–H) = 7.1 Hz, J(P–H) = 14.0 Hz, 6, P(CH(CH3) (CH3))2), 1.05 (dd, J(H–H) = 7.1 Hz, J(P–H) = 15.1 Hz, 6, P(CH(CH3)(CH3))2). 31P NMR (CDCl3): d 54.0. 13C NMR (CDCl3): d 133.2 (d, J(P–C) = 9.1 Hz, Ph2,6), 132.5 (d, J(P–C) = 33.2 Hz, Ph1), 128.5 (CN), 128.2 (d, J(P–C) = 8.8 Hz, Ph3,5), 75.4 (Cp), 27.5 (d, J(P–C) = 22.0 Hz, P(CH(CH3)2)2), 18.9 (s, 2C, P(CH (CaH3)2)2), 18.6 (s, P(CH(CbH3)2)2), 4.3 (s,CH3CN).
Elemental analysis for ½CpðPri2PhPÞRuðNCCH3Þ2½PF6, C21H30F6N2P2Ru (587.484). Anal. Calc.: C, 42.93; N, 4.77;
H, 5.15. Found: C, 42.87; N, 4.53; H, 5.36%.
3.3. [Cp(PriPh2P)Ru(NCCH3)2][BF4]
Prepared analogously to½CpðPri3PÞRuðNCCH3Þ2½BF4, using PPriPh2(0.290 g, 1.27 mmol) and [CpRu(NCCH3)3] [BF4] (0.480 g, 1.27 mmol). Yield: 0.670 g (93%). The corre- sponding PF6 salt was prepared with a similar yield. IR (Nujol): m(CN) = 2276 cm1. 1H NMR (CDCl3): d 7.47–
7.37(m, 10, Ph), 4.27 (s, 5,C5H5), 2.76 (m, 1, P(CH(CH3)2)), 2.34 (s, 6, CH3CN) 1.10 (dd, J(H–H) = 7.1 Hz, J(P–H) = 15.5 Hz, 6, P(CH(CH)3)). 31P NMR (CDCl3):d 51.3. 13C NMR (CDCl3): d 133.9 (d, J(P–C) = 38.4 Hz, i-Ph), 133.0 (d, J(P–C) = 9.9 Hz, o-Ph), 129.9 (d, J(P–C)
= 2.2 Hz, p-Ph), 128.3 (d, J(P–C) = 9.0 Hz, m-Ph), 128.1 (CH3CN), 76.2 (s, Cp), 29.1 (d, J(P–C) = 24.2 Hz, P(CH(CH3)2)), 18.8 (s, P(CH(CH3)2)), 4.2 (s,CH3CN). Ele- mental analysis for [Cp(PriPh2P)Ru(NCCH3)2][PF6], C24H28F6N2P2Ru (621.501). Anal. Calc.: C, 46.83; N, 4.51;
H, 4.54. Found: C, 46.77; N, 4.87; H, 4.74%.
3.4. [Cp(Ph3P)Ru(NCCH3)2][BF4] [21]
This complex was prepared analogously to½CpðPri3PÞRu ðNCCH3Þ2½BF4, using PPh3 (0.348 g, 1.35 mmol) and [CpRu(NCCH3)3][BF4] (0.500 g, 1.33 mmol). Yield:
0.750 g (94%). Characterization data agree with those reported in the literature.
3.5. [CpðPri3PÞRuH3]
LiAlH4 (0.090 mg, 2.4 mmol), recrystallized from diethyl ether, was added to a solution of ½CpðPri3PÞRu ðNCCH3Þ2½BF4 (0.470 g, 0.95 mmol) in 40 ml of THF.
The resulting solution was stirred overnight at ambient tem- perature and then slowly hydrolyzed with degassed water.
After evaporation of the solvent, the brown residue was extracted with hexane (3·10 ml). Removal of volatiles and recrystallization at 30C from ether/ethanol (2:1) afforded 0.200 g of CpðPri3PÞRuH3in the form of grey crys- tals, which deliquesce when brought to room temperature.
Yield: 63%. IR (Nujol): m(Ru–H) = 2010 cm1. 1H NMR (toluene-d8): d 4.94 (s, 5, C5H5), 1.42 (d sept, J(H–H) = 7.0, J(P–H) = 9.2 Hz, 3, P(CH(CH3)2)3), 0.95 (dd, J(H–H) = 7.0 Hz, J(P–H) = 13.6 Hz, 9, PCH(CH)3), 11.26 (d, J(P–H) = 20.5 Hz, 3, RuH3). 31P (toluene-d8):
d 103.0. 13C (toluene-d8): d 81.5 (s, C5H5), 30.1 (d, 7J(P–C) = 30.2 Hz, PCH(CH3)2), 28.9 (d, J(P–C) = 25.6 Hz, PCH(CH3)2). Elemental analysis for C14H29RuP (329.42). Anal. Calc.: C, 51.04; H, 8.87. Found: C, 51.10;
H, 8.95%.
3.6. [CpðPri2PhPÞRuH3]
This complex was prepared analogously to CpðPri3PÞ RuH3 with LiAlH4 (0.100 g, 2.6 mmol) and ½CpðPri2PhPÞ RuðNCCH3Þ2½BF4 (0.550 g, 1.03 mmol). Yield: 0.320 g (85%). IR (Nujol): 2009 cm1. 1H NMR (CD2Cl2): 7.79 (m, 2, o-Ph), 7.36 (m, 3,m-Ph and p-Ph), 5.08 (s, 5, Cp), 2.13 (dsept, J(H–H) = 6.8 Hz, J(P–H) = 9.5 Hz, 2 P(CH (CH3)2)2), 1.00 (dd, J(P–H) = 15.9 Hz, J(H–H) = 6.6 Hz, 6, P(CH(CaH3)2)2), 0.76 (dd, J(P–H) = 15.0 Hz, J(H–H) = 6.9 Hz, 6, P(CH(CbH3)2)2), 11.33 (d, J(P–H) = 20.1 Hz, 3, RuH3).31P NMR (CD2Cl2): 97.6 (s).
13C NMR (CD2Cl2): 134.1 (d, J(P–C) = 9.6 Hz, o-Ph), 129.5 (d,J(P–C) = 2.3 Hz,p-Ph), 127.6 (d,J(P–C) = 8.4 Hz, m-Ph), 82.0 (d, J(P–C) = 1.7 Hz, Cp), 26.5 (d, J(P–
C) = 31.7 Hz, P(CH(CH3)2)2), 19.5 (d, J(P–C) = 3.5 Hz, P(CH(CaH3)2)2), 18.8 (s, P(CH(CbH3)2)2). Elemental analysis for C17H27RuP (363.440). Anal. Calc.: C, 56.18; H, 7.49.
Found: C, 56.47; H, 7.88%.
3.7. [Cp(PriPh2P)RuH3]
This complex was prepared analogously to CpðPri3PÞRuH3 with LiAlH4 (0.101 mg, 2.7 mmol) and [Cp(PriPh2P)Ru(NCCH3)2][BF4] (0.600 g, 1.06 mmol).
Yield: 0.350 g (83%). IR (Nujol): 2001 cm1.1H NMR (C6D6): 7.65 (dt, J(H–H) = 6.9 Hz, 4, o-Ph), 7.03 (m, 6, m-Ph +p-Ph), 4.88 (s, 5, Cp), 2.25 (m, 1, CH), 0.92 (dd, J(H–H) = 6.6 Hz, J(P–H) = 16.8 Hz, 6, Me), 10.30 (d, J(P–H) = 20.1 Hz, 3 H). 31P NMR (C6D6): 87.0 (s).
13C NMR (C6D6): d 133.0 (d, 2J= 10.5 Hz, o-Ph), 128.1–127.5 (m, p,m-Ph), 82.7 (s, C5H5), 29.1 (d,
1J= 33.2 Hz, P(CH(CH3)2)), 18.8 (P(CH(CH3)2)). Elemen- tal analysis for C20H25RuP (397.456). Anal. Calc.: C, 60.44;
H, 6.34. Found: C, 61.34; H, 6.94%.
3.8. [Cp(Ph3P)RuH3]
This known complex [14] was prepared analogously to CpðPri3PÞRuH3, using LiAlH4 (0.088 g, 2,3 mmol) and [Cp(Ph3P)Ru(NCCH3)2]BF4 (0.550 g, 0.92 mmol). Yield:
0.246 g (62%).
3.9. Crystal structure determinations of1b
Colourless crystals of 1b were grown from hexane by cooling the solutions to 25 to 30C. Single crystal of 1b was coated by polyperfluoro oil and mounted directly to the Bruker Smart three-circle diffractometer with CCD area detector at 123(2) K. The crystallographic data and characteristics of structure solution and refinement are
given in Table 1. The structure factor amplitudes for all independent reflections were obtained after the Lorentz and polarization corrections. A multi-scan absorption cor- rection was applied. The structures were solved by heavy- atom methods [24] and refined by full-matrix least squares procedures, using xðjF2oj jF2cjÞ2 as the refined function.
All hydrogen atoms were found from the difference map.
In the final cycles of refinement, all the non-hydrogen atoms were refined with anisotropic temperature parame- ters. The hydride ligands were refined isotropically, other hydrogen atoms were refined using the riding scheme.
The largest residuals in the final difference Fourier maps were small (0.788 and0.597 e A˚3), location and magni- tude of the residual electron density was of no chemical significance.
Acknowledgements
GIN thanks NSERC for financial support and CFI for a generous equipment grant. L.G.K. and J.A.K.H. thank the Royal Society (London) for a Joint Research Grant.
L.G.K. also thanks the Royal Society of Chemistry (Lon- don) for the RSC Journal Award for International Authors.
Table 1
Crystal data and structure refinement for1b Empirical formula C20H25PRu
Formula weight 397.44
Temperature 123(2) K
Wavelength 0.71073 A˚
Crystal system Monoclinic
Space group P2(1)/c
Unit cell dimensions
a(A˚ ) 11.7325(2)
b(A˚ ) 7.4373(2)
c(A˚ ) 20.1921(4)
a() 90
b() 97.3950(10)
c() 90
Volume ( A˚3) 1747.27(7)
Z 4
Dcalc(Mg/m3) 1.511
Absorption coefficient (mm1) 0.983
F(0 0 0) 816
Crystal size (mm3) 0.32·0.23·0.12 hRange for data collection () 1.75–30.01
Index ranges 156h616,96k610,
216l628 Reflections collected 11 968 Independent reflections [Rint] 5040 [0.0170]
Completeness to theta = 30.01 98.5%
Maximum and minimum transmission
0.8911 and 0.7437
Refinement method Full-matrix least-squares onF2 Data/restraints/parameters 5040/0/299
Goodness-of-fit onF2 1.065
FinalRindices [I> 2r(I)] R1= 0.0236,wR2= 0.0587 Rindices (all data) R1= 0.0278,wR2= 0.0612 Largest difference in peak and hole
(e A˚3)
0.788 and0.597
Appendix A. Supplementary material
CCDC 647983 contains the supplementary crystallo- graphic data for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retriev- ing.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jorganchem.
2007.07.024.
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